George Monbiot is a case in point, in an article on how stoopid Americans aren't sophisticated enough to embrace their intellectual liberal superiors, a theory which I've debunked before, he claims:
One theme is both familiar and clear: religion - in particular fundamentalist religion - makes you stupid. The US is the only rich country in which Christian fundamentalism is vast and growing.
This is nonsense. The most educated regions of the US, based on academic performance and the location of elite universities are the most secular parts so superficially this makes sense. Yet 300 years ago New England and the North East were the most religiously observant parts of what would become the USA, the Puritans of New England were far more devout that the Presbyterians of Appalachia which is why they were so keen on executing witches in the North East. Yet even then New England had higher literacy rates and had established Harvard. So clearly Monbiot's claim is nonsense.
The contemporary example of heavily Mormon Utah ought to dispel the idea that religious observance makes you stupid as it is one of the most educated and economically successful states in the US.